1. Field of the Invention
The present invention relates to an external stimulus indicator for indicating the temperature/time history of a predetermined article (referred to hereinafter as a temperature/time history indicator) and in particular to an external stimulus indicator for indicating the temperature/time history in a production process (referred to hereinafter as process check label) or the temperature/time history in a distribution process (referred to hereinafter as distribution history indication label).
The present invention relates to an external stimulus indicator that upon application of external force, can indicate deformation or the level of deformation (quantity of deformation) (referred to hereinafter as deformation level indicator).
The present invention relates to an external stimulus indicator that can detect and indicate the change in polymer morphology by an external stimulus (referred to hereinafter as morphology change indicator).
More specifically, the present invention relates to an external stimulus indicator including a polymer composition composed of a polymer and a dye, wherein the polymer composition has the dye fixed in a specific molecular dispersion state in the polymer, and when kept at a temperature not lower than a specific temperature for at least a predetermined time or deformed to at least a certain level by external force, changes its color to a hue different from the initial hue thereof. The present invention also relates to a method of indicating the history of temperature and time or the quantity of deformation by external force experienced by a predetermined article by applying the indicator to the predetermined article. Further, the present invention relates to a method of detecting the deformation, or the level of deformation, of an article composed of a polymer molded body, by using the deformation level indicator.
2. Description of the Background Art
For example, products sensitive or undurable to heat need attention with regard to storage. Particularly, products such as chemicals sensitive to heat are made unusable once storage maximum temperature is exceeded. When such products are stored, their storage state can be confirmed with e.g. a temperature indicating label as a quality indicating medium. For example, there are materials including inorganic compounds that release water of crystallization upon heating, such as CoCl2.(CH2)6N4.10H2O, organic compounds that change their structure upon heating, such as spiropyran, and a system composed of 3 components (that is, a leuco dye, a solid acid, and a compound having an alcoholic hydroxyl group) that undergoes chemical change etc. upon heating, thereby being colored or decolored to indicate a change in temperature.
For example, a temperature indicating sheet for frozen food is known that has a structure in which a polyolefin nonwoven fabric impregnated with an agar aqueous gel, and if necessary a polyolefin nonwoven fabric, are sandwiched between a polyolefin film and a polyolefin film printed with a white oil-based ink containing a water-soluble dye and are jointed via an adhesive on the periphery thereof, wherein before freezing operation, the water-soluble dye is contained in the white oil-based ink and prevented from coloring, but after freezing and when the temperature of the content of the sheet is increased to thawing temperature, the water-soluble dye is dissolved with water exuded through fine pores in the nonwoven fabric, thereby coloring the white oil-based ink-printed face and readily indicating a change in the temperature of the content (see Japanese Patent Laying-Open No. 07-049656).
Further, a known example is a quality indicating medium capable of discriminating the heat history of the temperature environment in which it was stored, and it is constituted of a sheet wherein a liquid crystal/polymer composite membrane including liquid crystalline particles dispersed in a polymer matrix is sandwiched between two electroconductive substrates or between an electroconductive substrate and a protective layer, and wherein the liquid crystal is colored or decolored at a specific temperature, thereby allowing the quality indicating medium to be repeatedly usable in recording the heat history of the temperature atmosphere in which the medium was stored (Japanese Patent Laying-Open No. 11-237599).
Further, a known example is stationery that is provided with a layer in which a temperature-sensitive discoloring color-memory heat discoloration material that upon temperature change, shows hysteresis characteristics to shift the material from a colored to an uncolored state and vice versa or from one colored state to another colored state, wherein a two-phase-retention region in which the two phases of colored and uncolored states can coexist is in the ordinary temperature range, is firmly fixed in a dispersed state in a reversibly thermally discoloring layer, thereby changing a color, a design etc. thereon by an easy means such as change in outside air temperature, contacting with the fingers or friction, to enable disappearance or appearance of various images, thus not only demonstrating a temperature indicating effect but also contributing to design diversification and differentiation (Japanese Patent Laying-Open No. 09-295489).
Furthermore, a known example is a temperature indicating label that includes a support laminated thereon with a heat-sensitive recording layer, a permeable layer composed primarily of a pigment and a binder, a layer containing microcapsules encapsulating a heat-sensitive substance having a melting point of 0° C. or more, and a protective layer in this order, and it records automatic recognition information such as bar code on the heat-sensitive recording layer in a mild thermal environment or in a refrigerating/freezing room, and just before being stuck in a refrigerating/freezing room, is subjected to destruction of the microcapsules by pressurization and then stuck onto a frozen/refrigerated product, thereby irreversibly changing previously recorded images upon exposure of the frozen/refrigerated product to a predetermined temperature of 0° C. or more (Japanese Patent Laying-Open No. 2004-184920).
These conventional indicators that indicate the presence or absence of temperature change are extremely complex in their constitution, and even if experienced temperature can be indicated, they cannot indicate the history of elapsed time at that temperature. Accordingly, it has been desired to provide an indicator that is simple in constitution and can indicate both temperature and time history at that temperature.
Meanwhile, Japanese Patent Laying-Open No. 2005-87057 discloses a method of detecting nucleic acid molecule morphology, including intercalating an immobilized nucleic acid molecule with a dye and then detecting a change in the nucleic acid morphology, from a change in the intensity of fluorescence generated from the dye.